<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>10、检测函数或代码运行时长</title>
</head>

<body>
  <script>
    var start = Date.now();
    for (let arr = 0; arr < 10000; arr++) {
      console.log(arr)
    }
    var end = Date.now();
    alert(end - start);
  </script>
</body>

</html>